The Morse code error signal: eight dits and what comes next
The Morse code error signal is eight dits sent as one even run, ........, said di-di-di-di-di-di-di-dit. It means “that was wrong, ignore it”, and it is followed by the word you were sending, sent again from its first letter. It is written HH, because eight dits is two H’s run together with no letter gap, and in angle brackets it appears as <HH>, the way other prosigns are written.
It is one of the easiest signals to recognize and, oddly, one of the harder ones to send well. Here is why it is eight, how to keep it clean, what comes after it, and the shortcuts operators often take instead.
Why eight dits
Count up from one dit and look at what each run means:
| Dits | Code | What it is |
|---|---|---|
| 1 | . |
E |
| 2 | .. |
I |
| 3 | ... |
S |
| 4 | .... |
H |
| 5 | ..... |
the figure 5 |
| 6 or 7 | no character | |
| 8 | ........ |
the error signal |
Everything up to five dits is a real character, and a common one. Eight sits well clear of all of them, so a receiver who hears a long, even run of dits knows it is not a character as soon as it runs past five. That margin is the point: the error signal has to be impossible to confuse with text, because it is sent at exactly the moment the sender’s rhythm has already gone wrong.
The international standard for Morse (ITU-R M.1677-1) lists the error signal as eight dots, and that is what you should send. Like SOS, it is a prosign: one character, with only the one-unit gaps that belong inside a character.
In time, eight dits and seven gaps make 15 units. At 20 WPM, where a dit is 60 ms, the whole signal lasts 900 ms. At 12 WPM it takes 1.5 seconds.
Send it evenly
The danger with eight dits is a pause in the middle. Morse reads silence as structure, so a gap in the wrong place turns the error signal into letters:
| What you sent | What the receiver hears |
|---|---|
........ |
the error signal |
.... .... |
H H |
... ..... |
S 5 |
.. ...... |
I, then something unreadable |
A three-unit pause anywhere in the run breaks it. So keep the speed you were already sending at and let the dits flow at the same pace from first to last. Do not slow down to count them, which tends to open up gaps, and do not rush them into a buzz, which makes them hard to hear as separate dits.
On paddles this is easy: hold the dit paddle and the keyer sends perfectly even dits; you only have to let go after eight. On a straight key, eight in a row is longer than any run inside an ordinary character, and your wrist will want to bunch them. It is worth practicing on its own, a few times a session, until it comes out as one smooth burst. Your fist in Morse code has more on evening out your keying.
What to send after it
After the error signal, leave a short gap, then resend the word you were sending, from its first letter. Do not try to pick up from the letter that went wrong; a whole word is easier for the receiver to take in than a fragment.
An example. You mean to send MEET AT NOON. You get as far as NOO, your hand slips, and you send K instead of N. On the air it goes like this:
MEET AT NOOK HH NOON
The receiver hears MEET AT, then NOOK, then the error signal, then NOON. They cross out NOOK, write NOON, and carry on. The written line above uses letters for clarity; the HH is sent as eight dits with no gap in the middle.
A few cases call for judgment:
- The slip was in the word before. If you notice a mistake only after you have finished the word, send the error signal and go back to the word with the mistake, then continue from there.
- The slip does not change the meaning. If you send NOOON and the meaning is plain, many operators let it go rather than break the flow. That is a choice, not a rule.
- Numbers, names and callsigns. Always correct these. Context cannot fix a wrong figure in a time, a signal report or a callsign, and a receiver cannot guess which digit you meant.
On the air: what operators often do
On the air, many operators skip the full signal for small slips. They often stop for a moment, leave a clear pause, and send the word again; the receiver hears the repeat and keeps the second version. In a friendly, unhurried contact this is common, and nobody minds.
Others send a run of dits that is not exactly eight. A receiver will usually still understand it, since any long run of dits is plainly not a letter, but eight is the signal, and sending it properly costs you nothing.
The error signal is for the sender’s own mistakes. When the receiver is the one who missed something, the tools are different: a question mark on its own, or the abbreviations AGN (again), RPT (repeat) and PSE (please), as in PSE RPT. CW abbreviations: CQ, DE, 73, TU and more lists those and the others you will hear in a contact.
Copying it on the receiving end
When you are writing down what you hear, the error signal tells you to throw away the word in progress. The quickest habit is a single line through it, then write the resent word straight after. Do not erase; you need to keep your pencil moving.
When you are copying in your head, the move is the same: drop the half-heard word and wait for the next one. Some learners freeze when they hear a long run of dits and try to count it. You do not need to. Anything past five dits is not a character, so as soon as the run keeps going, you know what it is.
If you are learning, it helps to practice both ends. Send a sentence to yourself, put a deliberate slip in it, send the error signal and the word again, then play it back or have a friend copy it. Hearing your own correction is a good way to find out whether it came out as eight even dits or as H H.
The error signal on a Mac
The same signal is useful away from the radio. In Dot & Dash, the error signal is part of the course: chapter 20 teaches SK and the error signal together. With Type Anywhere switched on, you key Morse on a modifier key (Right Option by default) and it is typed into the app in front, and there the error signal deletes the last word Dot & Dash typed, never text you typed yourself. AR, BT and SK type nothing. How to type Morse code into any app on a Mac explains the setup.
Questions
Is the Morse code error signal exactly eight dits?
Yes. The ITU’s error signal is eight dots sent as one character. A long, even run of dits is recognized even when the count is off, but eight is the standard and is what you should send.
Why is the error signal written HH?
Because H is four dits, ...., and the error signal is two H’s run together with no letter gap between them. Like other prosigns, it is written with a bar over the letters or as <HH>.
What do I send after the error signal?
Resend the word you were sending, from its first letter. If the mistake was in an earlier word, go back to that word and continue from there.
Can I just pause and resend instead?
On the air, operators often do exactly that for a small slip, and receivers follow it fine. The error signal is clearer, though, and it is the better habit when you are learning or when the word was a number or a callsign.